CN102405091A - A method of reducing flue gas emissions and a boiler - Google Patents

A method of reducing flue gas emissions and a boiler Download PDF

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Publication number
CN102405091A
CN102405091A CN2010800171274A CN201080017127A CN102405091A CN 102405091 A CN102405091 A CN 102405091A CN 2010800171274 A CN2010800171274 A CN 2010800171274A CN 201080017127 A CN201080017127 A CN 201080017127A CN 102405091 A CN102405091 A CN 102405091A
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boiler
flue gas
reducing agent
furnace
heat exchanger
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CN102405091B (en
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帕西·米库莱宁
劳里·帕卡里宁
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Andritz Oy
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Andritz Oy
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J15/00—Arrangements of devices for treating smoke or fumes
    • F23J15/003—Arrangements of devices for treating smoke or fumes for supplying chemicals to fumes, e.g. using injection devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/54—Nitrogen compounds
    • B01D53/56—Nitrogen oxides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B21/00—Water-tube boilers of vertical or steeply-inclined type, i.e. the water-tube sets being arranged vertically or substantially vertically
    • F22B21/34—Water-tube boilers of vertical or steeply-inclined type, i.e. the water-tube sets being arranged vertically or substantially vertically built-up from water tubes grouped in panel form surrounding the combustion chamber, i.e. radiation boilers
    • F22B21/341—Vertical radiation boilers with combustion in the lower part
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B21/00—Water-tube boilers of vertical or steeply-inclined type, i.e. the water-tube sets being arranged vertically or substantially vertically
    • F22B21/40—Water-tube boilers of vertical or steeply-inclined type, i.e. the water-tube sets being arranged vertically or substantially vertically built-up from water tubes arranged in a comparatively long vertical shaft, i.e. tower boilers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B31/00—Modifications of boiler construction, or of tube systems, dependent on installation of combustion apparatus; Arrangements of dispositions of combustion apparatus
    • F22B31/04—Heat supply by installation of two or more combustion apparatus, e.g. of separate combustion apparatus for the boiler and the superheater respectively
    • F22B31/045—Steam generators specially adapted for burning refuse
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22D—PREHEATING, OR ACCUMULATING PREHEATED, FEED-WATER FOR STEAM GENERATION; FEED-WATER SUPPLY FOR STEAM GENERATION; CONTROLLING WATER LEVEL FOR STEAM GENERATION; AUXILIARY DEVICES FOR PROMOTING WATER CIRCULATION WITHIN STEAM BOILERS
    • F22D1/00—Feed-water heaters, i.e. economisers or like preheaters
    • F22D1/02—Feed-water heaters, i.e. economisers or like preheaters with water tubes arranged in the boiler furnace, fire tubes, or flue ways
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/20—Reductants
    • B01D2251/206—Ammonium compounds
    • B01D2251/2062—Ammonia
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/20—Reductants
    • B01D2251/206—Ammonium compounds
    • B01D2251/2067—Urea
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
    • F23G2209/00—Specific waste
    • F23G2209/10—Liquid waste
    • F23G2209/101—Waste liquor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J2215/00—Preventing emissions
    • F23J2215/10—Nitrogen; Compounds thereof
    • F23J2215/101—Nitrous oxide (N2O)
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00—Combustion technologies with mitigation potential
    • Y02E20/12—Heat utilisation in combustion or incineration of waste
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P80/00—Climate change mitigation technologies for sector-wide applications
    • Y02P80/10—Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier
    • Y02P80/15—On-site combined power, heat or cool generation or distribution, e.g. combined heat and power [CHP] supply

Abstract

The present invention relates to a method and a boiler for decreasing the amount of nitrogen oxides in flue gases of a boiler, which flue gases are generated in the combustion of fuels and air. The boiler has a water circulation system comprising superheaters (8) and a furnace (1) for combustion of fuel and for generating flue gases that contain nitrogen oxides, which flue gases mainly flow upwards in the furnace and further to the superheater zone and via other heat recovery surfaces of the boiler out of the boiler, and a nitrogen oxides reducing agent is introduced into the flue gases.; It is essential that the nitrogen oxides reducing agent is introduced into the flue gases prior to the superheater zone, before which the temperature of the flue gases is decreased by means of at least one heat exchanger (15) that is located in the flue gas flow upstream of the introduction of the reducing agent, for obtaining a suitable temperature window in the flue gas flow in order to reduce nitrogen oxides.

Description

Reduce the method and the boiler of fume emission
Technical field
The present invention relates to the method for a kind of minimizing from the amount of the nitrogen oxide of the flue gas of boiler, this nitrogen oxide produces in the combustion process of fuel and air or other oxygen-containing gas.The invention still further relates to the boiler that produces steam.
Background technology
The flue gas that produces the boiler (the for example recovery boiler of chemical pulping factory) of steam is derived and is contacted with water preheater with various heat exchangers, superheater, the boiler tube bundle (bank) [w1] of boiler from burner hearth (furnace), thereby reclaims the heat that contains in the flue gas in the water, steam and their mixture that in heat exchanger, flow.Boiler tube bundle is meant a kind of heat exchanger with heat exchange element, and its internal flow boiler water to be heated.The economizer of boiler (preheater) is meant a kind of heat exchanger with heat exchange element, and its internal flow boiler feedwater to be heated.Keeping the free space that supplies flow of flue gas in boiler tube bundle between heat exchanger element and the economizer.When flue gas flows through heat exchanger element, in the feedwater or boiler water that transfer of heat flows to element internal.The flue gas of boiler is drawn out to boiler at the back gas cleaning plant, for example electrostatic precipitator via the fume emission pipeline from economizer with a kind of mode known per se.
Fig. 1 diagram has the structure of the chemical recovery boilers of burner hearth 1, and burner hearth 1 limits on water-cooling wall (antetheca 2, sidewall 3 and rear wall 4) and the bottom 5 that water pipe forms.Combustion air is sent into burner hearth from some different levels as first air, second air and the 3rd air.The air that also can have other levels.Waste liquid (for example black liquor) is drawn via the nozzle 6 between second air zone and the 3rd air zone.In combustion process, waste liquid forms the fused mass bed on the bottom 5 of burner hearth, and from the fused mass bed fused mass is discharged from burner hearth bottom via fused mass outflow groove (spout) 7 that adapts in the lower furnace portion.
Above burner hearth, be provided with heating surface (being superheater 8), and heat exchanger (boiler tube bundle 9 with economizer 10) following the superheater that is positioned at the burner hearth top, and be positioned on the side of rear wall 4.The heat that produces in the burner hearth reclaims in said boiler tube bundle and economizer.On boiler tube bundle 9, the water that is in saturation temperature partly is vaporized into steam; And before the steam of water being introduced boiler produced part 9 and superheat section 8, water was heated in feed water preheater 10 by means of flue gas.In superheater, saturated vapor is heated under higher temperature, thereby produces steam.So-called furnace arch, furnace nose (bullnose) marks with Reference numeral 14.
Water/the vapor recycle of boiler is arranged to carry out through Natural Circulation; Through this circulation; Water/the vapour mixture that in the water pipe of hearth wall and burner hearth bottom, forms rises via collector [w2] and gets into steamdrum (steam drum) 11, and said steamdrum 11 is with respect to crisscross location (promptly being parallel to antetheca 2), boiler edge.Hot water flows in the manifold [w3] 13 on the bottom from steamdrum via down-comer 12, and water branches in the water pipe of bottom, in the stepping entry tube wall of going forward side by side from manifold again.
Spent liquor recovery boiler is formed by schematically illustrated following critical piece among Fig. 1 usually:
-lower furnace portion 16, the burning of waste liquid is mainly here carried out.
-burner hearth middle part 17, the final burning of the combustible of gas form is mainly here carried out.
-upper furnace 18
-superheater district 8, the saturated vapor that wherein flows out steamdrum 11 is converted into (overheated) steam with higher temperature.In superheater district or its upper reaches, be typically provided with the so-called screen system 15 that is commonly used to vaporize water.
-boiler tube bundle 9 (being water vaporizer), the water that wherein is in saturation temperature partly is vaporizated into steam.
-feed water preheater (being so-called economizer) 10, wherein before the steamdrum 11 of water being introduced boiler, steam produce part 9 and superheat section 8, the feedwater of in heat transfer element, flowing by means of flue gas by preheating.
-bottom is that water, top are the steamdrum 11 of saturated vapor.Some boiler has two steamdrums: steamdrum (going up steamdrum) He Shuibao (following steamdrum) is provided with the heat transfer element that is used for vaporize water, promptly so-called boiler tube between the two.
Furnace arch, furnace nose is located at the place, top of the burner hearth on the boiler rear wall, and furnace arch, furnace nose is the place that boiler narrows down, and it is the common edge battery limit (BL) between burner hearth and the heating surface.Furnace arch, furnace nose is formed by the depressed part in the rear wall of boiler, and this depressed part points to the antetheca of boiler.Therefore, furnace arch, furnace nose comprises: the lower wall part, and this part is obliquely pointed to the boiler antetheca from rear wall usually; Upper wall portion, this part is obliquely pointed to rear wall from the boiler antetheca; With furnace arch, furnace nose vault or end that these parts are combined.The regional effect of furnace arch, furnace nose is that protection superheater part does not receive the direct heat radiation of burner hearth, and it is mobile towards the fume emission pipeline of boiler to help upwards mobile flue gas to walk around the turning, makes flue gas pass through heating surface equably.The so-called furnace arch, furnace nose degree of depth (it flows into upper furnace for the guiding flue gas and plays an important role) for example is generally the 40-50% of burner hearth total depth (horizontal length that refers to burner hearth sidewall) in the boiler of single steamdrum.
Many recovery boilers additionally are provided with the upper reaches screen casing that is positioned at superheater along gas flow direction (usually flatly) in the bosom of furnace arch, furnace nose.Usually, steam and water saturation mixture flow in screen casing, and said screen casing is connected with the water circulation of boiler.The purpose of screen casing is before flue gas gets into the superheater district, it to be cooled to a certain degree, preventing the heat radiation of burner hearth to superheater tube, and so-called carrying under one's arms (carry over) particle that keeps a part to overflow from burner hearth.
In the burning of various fuel (for example black liquor), produce a large amount of flue gases that comprises various impurity (for example nitrogen oxide).In combustion process, nitrogen oxide is produced by a part of nitrogen that carries in the air and fuel, and remaining nitrogen is then with dinitrogen (N 2) form and a spot of harmfulness compound (for example, nitrous oxide (N 2O), ammonia (NH 3) and hydrogen cyanide (HCN)) form discharge.Nitrogen oxide forms via some kinds of different approaches, and this depends on condition and fuel.
The purpose that is used to remove the method for nitrogen oxide is that the emission of the nitrogen oxide of pollution is minimized, thereby makes harmless dinitrogen N 2Part maximization, the discharge capacity with every other hazardous compound remains on low-level simultaneously.Typical nitrogen oxide removal method comprises fuel staging, air classification and SNCR (SNCR).
SNCR is to reduce the nitrogen oxide that is produced in the burning through adding reagent (for example ammonia).The efficient of this method receives the influence of operating condition, fuel composition and existing reagent.Therefore, this technology provides known embodiment, comprising the poor fuel engineering [United States Patent (USP) 3 that uses ammonia; 900,554], use the rich fuel engineering [United States Patent (USP) 4,325 of ammonia; 924] and use the rich fuel engineering [United States Patent (USP) 4,335,084] of urea.
The SNCR modification comprises through various streams adds reducing agent, for example adds with reburning fuel, adds with air, or adds separately.The operation of every kind of modification is confined to exactly determined condition.Under the situation that does not have carbon monoxide (CO), poor fuel SNCR operates in the temperature range of 1100-1400K (827-1127 ℃), then operation under higher temperature of rich fuel SNCR.Yet, in utilizing nearly all technology of SNCR method, all have carbon monoxide, and its harmful result makes temperature window skew and narrowing down.In some kinds of combustion apparatus, very difficult creation is used for the optimum condition of SNCR.
United States Patent (USP) 5820838 has been described a kind of CFBB, and wherein heat transfer pipe (for example Ω pipe) is installed in the flue gas stream.In this solution, be used for injecting device with the reagent (like ammonia or urea) of reaction of nitrogen oxides by integrated in the Ω pipe.Purpose is in order when injecting, to obtain enough low temperature (as the 100-600 ℃) cooling to reducing agent, to make reducing agent not decompose.Yet, in this patent, do not have to note between nitrogen oxide and reducing agent, to create suitable temperature window.
Be implemented in the recovery boiler minimizing to the NOx content through method based on classification or SNCR technology; These technology are used: " the 4th air " that i) in recovery boiler top, is positioned at the high height place; In an one of which embodiment, add ammonia and be entrained in (WO 97/21869) in the said air; Ii) " vertical air classification " [FI 101420 B] send into air-flow by means of the nozzle that is positioned at a plurality of vertical height place the burner hearth of recovery boiler in this technology; Iii) " Mitsubishi advanced combustion technology " (MACT) [Arakawa Y., Ichinose T., Okamoto A.; Baba Y, Sakai T., in Proc.of the Int.Chemical Recovery Conf.; Whistler, British Columbia, Jun.11-14; 257-260,2001], can after air classification, add reducing agent (urea) in this technology; And iv) black liquor classification [patent FI 103905], in this technology black liquor is highly sent in the burner hearth with basis vertical air classification (ii) from least two.By means of these technology, reached the NOx percent reduction of 30-50%, but in practice, needing not that best part is regulated for recovery boiler.The temperature that these technology often need oversized burner hearth to be used to remain on after the burner hearth is enough low, and/or need more expensive material solution prevent corrosion.In practice, fractional combustion in recovery boiler or SNCR specification requirement temperature are low to moderate 850-1000 ℃, and only in the recovery boiler bigger and therefore more expensive than conventional boiler, just can reach this temperature.
Summary of the invention
An object of the present invention is to provide a kind of method, this method is used to control the discharging from the harmful nitrogen compound (especially nitrogen oxide) of combustion process entering with the mode more effective and more more economical than said method.Especially, the purpose of this invention is to provide a kind of method and a kind of equipment of arranging suitable temperature window based on the method for SNCR technology removal nitrogen oxide that is used to.The present invention especially can be applied in the chemical recovery boilers, but also can be applied in other boilers that produce steam, and these boilers need be created the required temperature window of SNCR technology.
In order to realize these purposes; The present invention relates to the method for a kind of minimizing from the amount of the nitrogen oxide of the flue gas of boiler; This nitrogen oxide produces in the combustion process of fuel and air; Said boiler has the water circulation system that comprises superheater and is used for the burner hearth that combustion fuel also produces the flue gas that contains nitrogen oxide; Said flue gas upwards flows in burner hearth substantially, and further flow to the superheater district and flow out boiler via other heating surfaces of boiler, and in said flue gas, introduces the reagent that is used for nitrogen oxides reduction.The invention is characterized in; NOx reducing agent is introduced in the flue gas in the superheater district before; Reduce the temperature of flue gas before this by means of at least one heat exchanger of the flue gas at the upper reaches that are positioned at reducing agent introducing place stream; Be used in flue gas stream, obtaining suitable temperature window, so that nitrogen oxides reduction.
In addition, the present invention relates to a kind of boiler that produces steam, this boiler has: water circulation system, this water circulation system comprise heating surface (heat recovery surfaces) (for example superheater); Burner hearth, said burner hearth are used for combustion fuel and produce flue gas, and said flue gas upwards flows in burner hearth substantially, and further flow to the superheater district and flow out boiler via other heating surfaces; And feed arrangement, this feed arrangement is used for introducing the reagent that is used for reducing at the nitrogen oxide of flue gas.The invention is characterized in: one or more heat exchangers are arranged in the flue gas stream of burner hearth, are used for reducing the temperature of flue gas and are used for creating the suitable temperature window that is used for nitrogen oxides reduction at flue gas stream; And the feed arrangement that is used for reducing agent is after the flow of flue gas direction is positioned at one or more heat exchangers and before the superheater district.
In this regard, heat exchanger is meant that ground connection is recovered to a kind of equipment the medium with heat from flue gas therebetween.Usually, this equipment comprises pipeline, and the medium that receives heat from flue gas flows at this pipe interior.
According to a preferred embodiment of the invention, in said heat exchanger or hot surface, heat is recovered to the water circulation system of boiler from flue gas, is used for superheated steam and/or gasifying boiler water and/or preheating feedwater.Also can reclaim heat, be used for the combustion air of heating boiler and/or heat other medium by means of heat exchanger.Essential characteristic of the present invention is: heat is recovered to the heat exchanger that is installed in the upper furnace from flue gas; The quantity of said heat exchanger is at least one; Thereby the temperature of flue gas is reduced, make it to be suitable for reducing the content of nitrogen oxide by means of reducing agent (such as ammonia).
Importantly, said one or more heat exchangers are positioned at such some place, are formed with enough volumes at this some place, are used for feeding reagent and under proper temperature, react before the superheater district that is usually located at above the furnace arch, furnace nose with being used for.
As previously mentioned, boiler (especially chemical recovery boilers) can be provided with a screen casing at the superheater upper reaches along the flow of flue gas direction, and these screen casings flatly are arranged in the bosom of furnace arch, furnace nose usually.In structure according to the present invention; Said heat exchanger can be the screen system that is positioned at such height place according to a preferred embodiment along the burner hearth vertical direction; Highly locate at this, be formed with the space that is beneficial to injection SNCR reagent in the screen system of the flue gas stream at the upper reaches that are arranged in the superheater above the furnace arch, furnace nose.
As previously mentioned, the furnace arch, furnace nose of boiler forms depressed part in the rear wall of boiler, and this depressed part points to the antetheca of boiler.Therefore, furnace arch, furnace nose comprises the lower wall part, and this part is obliquely pointed to the boiler antetheca from rear wall usually; Upper wall portion, this part is obliquely pointed to rear wall from the boiler antetheca; Also can be the furnace arch, furnace nose vault or the end of upright substantially wall part (the vertical part of boiler rear wall).According to embodiments of the invention, said at least one heat exchanger (for example screen casing) is positioned at the furnace arch, furnace nose below along the facade direction of boiler.According to the shape of furnace arch, furnace nose, at least one heat exchanger (for example screen casing) can also be positioned at the furnace arch, furnace nose zone according to embodiments of the invention.In this case, the end of furnace arch, furnace nose is preferably formed by the vertical wall part that lower wall and upper wall with above-mentioned inclination combine, and makes furnace arch, furnace nose zone long enough vertically, to be used to be provided with one or more heat exchangers.
In solution according to the present invention; One or more heat exchangers will be positioned in the superheater a distance from its top; So that feeding is used for the reagent of nitrogen oxides reduction in an advantageous manner between heat exchanger and superheater; Make said reducing agent that time enough and reaction of nitrogen oxides arranged, remove nitrogen oxide from flue gas with maximum possible degree ground before being used in the superheater district.Required separation distance receives the influence of the mixing efficiency and the flue-gas temperature of retention time, reducing agent and flue gas.
The invention has the advantages that the reagent (like ammonia or urea) that reacts with NOx can inject in large quantities, thereby obtains enough retention times under suitable temperature window.Through ammonia is evaporated in the air, this reagent can be introduced into (for example carrying secretly) in the air-flow of heat exchanger (for example screen casing) top, thereby obtains simultaneously effectively to mix.Another advantage of being worth mentioning is to have reduced the liquid particles (being the so-called particle of carrying under one's arms) that escapes on the superheater surface according to the position of screen casing of the present invention.
In solution of the present invention, preferably, serve as superheater along at least one heat exchanger that is positioned at the SNCR reagent decanting point upper reaches on the flow of flue gas direction.In other words, at least a portion of screen casing is delivered to heat the superheated steam from flue gas.Therefore, because screen casing has formed the part of required superheating surface capacity in the boiler, thereby the volume of the size of boiler or superheating surface can not increase.
The size that is positioned at said one or more heat exchangers at the SNCR reagent decanting point upper reaches is set as and makes flue-gas temperature fully reduce, and is used to obtain desired temperature window.Therefore, according to the present invention, a plurality of heat exchangers are arranged in flue gas stream, are in the upper reaches at the reaction of nitrogen oxides place in reagent and the flue gas, and these heat exchangers have enough capacity and are used for flue-gas temperature is reduced to suitable temperature window.
Allow to reduce the height of the superheater that is usually located at the furnace arch, furnace nose top according to solution of the present invention, thereby also reduce the total height of boiler.
Mainly only be delivered under the situation of hearth wall at heat, can make burner hearth and the whole boiler of boiler and boiler shop become very high thereby in the burner hearth of boiler, obtain desired temperature window.
The present invention allows to utilize SNCR technology, and the chemical recovery boilers or other steam boilers that especially are difficult to mix under desired temperature at the ammonia that injects or urea utilize the SNCR technology.
Through according to the present invention with the burner hearth at the upper reaches of the decanting point of the reagent (like ammonia) of NOx reaction at least one heat exchanger of installation; Obtained lower temperature; This allows in burner hearth, under suitable temperature window, to introduce reducing agent, thereby makes nitrogen oxide form the nitrogen G&W.This is problematic in the chemical recovery boilers of chemical pulping factory especially, because the temperature in the burner hearth of this boiler is too high for using the SNCR method usually.In addition, do not hope reducing agent process on superheating surface such as ammonia or urea, because the feeding that causes material under follow-up phase owing to corrosion of superheater is with unfavorable.Temperature in bubbling fluidized bed (BFB) boiler is usually less than the temperature in recovery boiler, but if desired, the present invention also can use by combining drum burble fluidized bed boiler.
The present invention allows for example effectively the reducing agent (for example urea and/or ammonia) that injects to be fed in the burner hearth with medium (like the flue gas of air or circulation) at the upper reaches of superheater; Thereby will protect superheater better, make it to avoid the possible corrosiveness of SNCR reagent.Is favourable with reducing agent with the combustion air feeding of boiler, because so just need not be provided for the additional openings of the said reagent of feeding for boiler.The carrier gas of reducing agent can be from the combustion-aid air system of boiler or independent special-purpose source of the gas.Can be as the flue gas of carrier gas from wherein using boiler of the present invention or from another boiler in the pulp mill.
Feeding can realize with the ammonia that also pressurizes with steam.Ammonia also can by means of steam jet ejector from container extract and with steam inject boiler together.Ammonia also can be liquefied, be mixed in the water and spray in the boiler.
In the feeding of reducing agent, medium also can be the combination of for example above-mentioned medium (like air and flue gas).
The invention provides the short-cut method of a kind of control from the discharging of the harmful nitrogen oxide compound of combustion process.
Description of drawings
The hereinafter with reference accompanying drawing is described the present invention in more detail, in the accompanying drawings:
Fig. 1 schematically illustrates chemical recovery boilers known per se; And
Fig. 2 a, 2b and 2c schematically illustrate some embodiments of the present invention.
Fig. 2 a-2c uses the Reference numeral identical with Fig. 1 at the place of being suitable for.
The specific embodiment
Fig. 2 a-2c diagram has the structure of the recovery boiler of the burner hearth that limits water wall (antetheca 2, sidewall 3 and rear wall 5) and the bottom 5 that water pipe forms.The superheater 8 of boiler is positioned at the burner hearth top.
-lower furnace portion 16, the burning of waste liquid is mainly here carried out.
-burner hearth middle part 17, the final burning of the combustible of gas form is mainly here carried out.
-upper furnace 18.
-superheater district 8, the saturated vapor that wherein flows out steamdrum is heated to form (overheated) steam with higher temperature.So-called screen system 15 is arranged on the furnace arch, furnace nose top along the flow of flue gas direction, is positioned at the upper reaches in superheater district.
The flue gas that in burner hearth, produces upwards flows into upper furnace and further flows to other heated portions of boiler, and for example superheater 8.The main flow direction of flue gas marks with arrow 19.
Furnace arch, furnace nose 14 is located at upper furnace 18 places on the boiler rear wall 4, and furnace arch, furnace nose is the place that boiler narrows down, and is the common edge battery limit (BL) between burner hearth and the heating surface.Furnace arch, furnace nose is formed by the depressed part in the boiler rear wall, and this depressed part points to boiler antetheca 2.Therefore, furnace arch, furnace nose comprises: lower wall part 14b, and this part is obliquely pointed to boiler antetheca 2 from rear wall 4 usually; Upper wall portion 14a, this part is obliquely pointed to rear wall 4 from boiler antetheca 2; With furnace arch, furnace nose vault that these parts are combined or terminal 14c.
Fig. 2 a diagram is according to heat exchanger of the present invention, and in this example down, screen casing 15 is arranged in the flue gas that upwards the flows stream 19 of furnace arch, furnace nose 14 belows of boiler.The feed arrangement 20 of reducing agent that is used for nitrogen oxide is between the lower limb 8a of screen casing and superheater 8.Screen casing 15 extends to rear wall from antetheca, thereby covers the level cross-sectionn of burner hearth, thereby screen casing is well contacted with the flue gas that upwards flows, and so can the temperature of flue gas be reduced to the level that helps nitrogen oxides reduction.In this embodiment, screen casing advantageously serves as superheating surface at least in part.Because screen section ground serves as superheating surface, thereby the part screen casing serves as the evaporation of water device.The size of serving as the screen casing of heat exchanger is set as the feasible temperature that fully reduces flue gas, so that obtain desired temperature window.
In the embodiment of Fig. 2 a, the heat exchanger of cooled flue gas is positioned at the furnace arch, furnace nose below, and reducing agent for example is introduced into the 3rd air.
The end of furnace arch, furnace nose also can be vertical substantially wall part 14c (Fig. 2 b and 2c).In this case, according to embodiments of the invention, heat exchanger or heat exchange surface (for example screen casing) are positioned at the zone of furnace arch, furnace nose end (Fig. 2 b).In this case, the end of furnace arch, furnace nose is preferably formed by the vertical wall part that lower wall that tilts and upper wall are combined, thereby the furnace arch, furnace nose zone vertically must be long concerning heat exchanger 15 being set and being used for that the device 20 of feeding reducing agent is enough.The distance of heat exchanger and superheater 8 must be enough, so that for nitrogen oxide and reducing agent was provided the enough reaction time before in the superheater district.
In the embodiment of Fig. 2 c, the end of furnace arch, furnace nose also is vertical substantially wall part 14c.The terminal zone of furnace arch, furnace nose is provided with and intersects and staggered screen casing 15a and the 15b that locatees, and this helps utilizing the space.Under this example, the device 20 that is used for the feeding NOx reducing agent also is arranged on the screen casing top.
In the embodiment of Fig. 2 b and 2c, reducing agent (for example ammonia) preferably is entrained in to be introduced in the air or introduces through circulating flue gas or with other mode mentioned above.
Allow in the boiler (in particular for remove the chemical recovery boilers of the method for nitrogen oxide based on the SNCR technology) that produces steam, to arrange suitable temperature window according to solution of the present invention.
Though preceding text have only been described some preferred embodiments according to the method for the invention, all such modifications and the modification that is included in claims restricted portion contained in the present invention.

Claims (18)

1. the method that produces of a combustion process that is used for reducing at fuel and air from the amount of the nitrogen oxide of the flue gas of boiler; Said boiler has the water circulation system that comprises superheater and is used for the burner hearth that combustion fuel also produces the flue gas that contains nitrogen oxide; Said flue gas upwards flows in said burner hearth substantially; And further flow to the superheater district and flow out said boiler via other heating surfaces of said boiler; And in said flue gas, introduce the reagent that is used for nitrogen oxides reduction
It is characterized in that; Said NOx reducing agent is introduced in the said flue gas in said superheater district before; Reduce the temperature of said flue gas before this by means of at least one heat exchanger of the flue gas at the upper reaches that are positioned at introducing place of said reducing agent stream; Be used in said flue gas stream, obtaining suitable temperature window, so that nitrogen oxides reduction.
2. method according to claim 1 is characterized in that, in said heat exchanger, reclaims heat from said flue gas and is used for superheated steam.
3. method according to claim 1 and 2 is characterized in that, in said heat exchanger, reclaims heat from said flue gas and is used for evaporation boiler water.
4. according to claim 1,2 or 3 described methods, it is characterized in that, in said heat exchanger, reclaim heat and be used for the preboiler feedwater from said flue gas.
5. according to each the described method in the aforementioned claim, it is characterized in that, in said heat exchanger, reclaim the combustion air that heat is used to heat said boiler from said flue gas.
6. according to each the described method in the aforementioned claim, it is characterized in that, said reducing agent is introduced said flue gas stream by means of medium.
7. method according to claim 6 is characterized in that, by means of air said reducing agent is introduced said flue gas stream.
8. method according to claim 6 is characterized in that, by means of the flue gas of circulation said reducing agent is introduced said flue gas stream.
9. according to each the described method in the aforementioned claim, it is characterized in that the said reducing agent that is used for nitrogen oxides reduction is ammonia, urea or the precursor that produces ammonia.
10. according to each the described method in the aforementioned claim, it is characterized in that black liquor burns in said burner hearth.
11. boiler that produces steam; Said boiler has water circulation system that comprises heating surface such as superheater and the burner hearth that is used for combustion fuel and generation flue gas; And be used for introducing the feed arrangement of said flue gas with being used for the reducing agent of nitrogen oxides reduction, said flue gas upwards flows in said burner hearth substantially, and further flow to the superheater district and flow out said boiler via other heating surfaces of said boiler; It is characterized in that; At least one heat exchanger is positioned at said burner hearth, is in the said flue gas stream, is used to reduce the temperature of said flue gas stream; So that in said flue gas stream, obtain to be used for the suitable temperature window of nitrogen oxides reduction, and the said feed arrangement that is used for said reducing agent is positioned at after said at least one heat exchanger and before said superheater district along said flue gas flow path direction.
12. boiler according to claim 11 is characterized in that, said boiler is provided with furnace arch, furnace nose, and the above burner hearth narrows down in the position of said furnace arch, furnace nose, and the facade direction of said at least one said boiler in heat exchanger edge is positioned at said furnace arch, furnace nose below.
13. boiler according to claim 11 is characterized in that, said boiler is provided with furnace arch, furnace nose, and the above burner hearth narrows down in the position of said furnace arch, furnace nose, and said at least one heat exchanger is positioned at the zone of said furnace arch, furnace nose along the facade direction of said boiler.
14. according to claim 10,11 or 12 described boilers; It is characterized in that; Said at least one heat exchanger is connected to said boiler water cycle system, makes that the steam that in said system, flows is overheated by means of the heat of said flue gas in said heat exchanger.
15. according to each the described boiler among the claim 10-14; It is characterized in that; The said device that is used for the said reducing agent of feeding is connected to the combustion-aid air system or the flue gas emission of said boiler, is used for the flue gas of combustion air or circulation is used as the carrier gas in the introducing of said reducing agent.
16. each the described boiler according among the claim 10-14 is characterized in that the said device that is used for the said reducing agent of feeding is connected to source of the gas, is used for said gas is used as the carrier gas in the introducing of said reducing agent.
17. according to each the described boiler among the claim 10-16; It is characterized in that; The said device that is used for the said reducing agent of feeding is connected to the flue gas emission of a certain other boilers, is used for the flue gas of circulation is used as the carrier gas in the introducing of said reducing agent.
18. each the described boiler according among the claim 10-17 is characterized in that said boiler is the chemical recovery boilers of chemical pulping factory.
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